Former New Zealand captain Martin Crowe has some words of wisdom for the Black Caps' embattled top order - that "batting six hours in a test is better than sex".

In an open letter to New Zealand's batting order published on Cricinfo, the world's most popular cricket website, Crowe delivered batting pointers to Brendon McCullum, Martin Guptill, Kane Williamson, Ross Taylor, Daniel Flynn and James Franklin, ahead of the second test against Sri Lanka, which starts in Colombo today.

In addition to directed advice to each of the six batsmen, Crowe called on the top order to "look in the mirror" and show more guts at the crease.

"Overall, lads, we just want a bit of individual spirit and some internal fortitude over a reasonable period at the crease," he wrote.

"Deep down I do hope you are thinking of churning out a ton. I know there is no greater feeling as a batsman. To bat six hours in a test is better than sex.

"Look in the mirror, remind yourselves of the affirmations you will need to control the concentration required for each ball, stick your chin up, and turn to face the music with fierce focus."

In the 1400-word piece, Crowe asked McCullum to reconsider his opening position for a spot further down the order, and show more discipline on defence.

To Taylor, he requested the captain "get back to the basics", while asking Guptill "stop beating yourself up". "Play to your strength of hitting straight, defensively and offensively. Make them suffer with your large frame and bat forming a wall they can't get through."

Crowe called on Williamson to work on his footwork, applauded Flynn's determination at the wicket, and asked Franklin why he wasn't playing his naturally attacking game. "Take some rescue remedy or smell some salts, but for heaven's sake, fire yourself up for the contest," he wrote.

Crowe wrote that the top order have looked flat in Sri Lanka, and implored them to "look within".

"Mostly I just want you to decide on who and what you are and what you know, what you bring to international cricket, what you want to give for your country," he wrote.

"From the outside, you look dispirited, disjointed and disoriented. Wrongly, you are looking outside for the answers.

"Look within, look in the mirror and ask yourself to stand up and be the men you are.

"Look within, be honest, strip away the rubbish and focus on what's important and what's really and essentially you."

Two weeks ago, Crowe was given a job by New Zealand Cricket as a "high-performance talent scout", whose brief is to watch domestic cricket in attempt to better identify rising potential young Black Caps.

He is currently facing a battle with cancer, after being diagnosed with lymphoma last month. The cancer is understood to be "treatable".